The mayor of Cleveland said on Thursday he did not agree with all of the U.S. Department of Justice’s findings in a scathing report on the widespread use of excessive force by the city’s police, saying it will take time to agree on how to reform the troubled department.

A federal investigation published this week concluded that Cleveland police supervisors tolerated, and in some cases, endorsed the use of unnecessary or unreasonable force.

The DOJ also found that officials who conducted internal reviews took pains to present the police officers involved in the best possible light.

“I’m not accepting things just because the DOJ said it,” Mayor Frank Jackson told reporters at a news conference.

He said the city would conduct a review of the DOJ’s conclusions to see which criticisms it agreed with, as it works out a consent decree with the federal government on how to reform policing.

“We will be delving into that, we will be reviewing that to see what is in there is accurate, which is inaccurate, which is a misstatement, which are examples that may be factual, may not be factual,” he said.

Jackson said the wider criminal justice system had to be reformed as well to do its job of holding police accountable for misconduct or wrongdoing.

The mayor also rejected calls for forced changes at the top of the police department, saying Cleveland Police Chief Calvin Williams has made changes to improve policing.

Jackson, who is in his third term as mayor, said he did not believe there was systemic failure in the police department.

But he did say: “There (are) significant problems that we have to address.”